Historically, many attempts have been made at developing and commercializing apparatus for the formation and uniform distribution of air laid fibers, be it staple textile fibers or cellulose pulp fibers.
All of these apparatus have been cumbersome, highly complex mechanical devices which have had several disadvantages in their operations. Several of these devices have actually been commercialized for the formation of fibrous webs or substrates in the non-woven industry.
Air forming of wood pulp fibrous webs has been carried out for many years; however, the resulting webs have been used for applications where either little strength is required, such as for absorbent products—i.e., pads—or applications where a certain minimum strength is required but the tactile and absorbency properties are unimportant—i.e., various specialty papers. U.S. Pat. No. 2,447,161 to Coghill, U.S. Pat. No. 2,810,940 to Mills, and British Pat. No. 1,088,991 illustrate various air-forming techniques for such applications.
In the late 1940's and early 1950's, work by James D'A. Clark resulted in the issuance of a series of patents directed to systems employing rotor blades mounted within a cylindrical fiber “disintegrating and dispersing chamber” wherein air-suspended fibers were fed to the chamber and discharged from the chamber through a screen onto a forming wire—viz., J. D'A. Clark U.S. Pat. Nos. 2,748,429, 2,751,633 and 2,931,076. However, Clark and his associates encountered serious problems with these types of forming systems as a result of disintegration of the fibers by mechanical co-action of the rotor blades with the chamber wall and/or the screen mounted therein which caused fibers to be “rolled and formed into balls or rice which resist separation”—a phenomenon more commonly referred to today as “pilling”. Additionally, J. D'A. Clark encountered problems producing a web having a uniform cross-direction profile, because the fiber input and fiber path through the rotary former was not devoid of cross flow forces.
The formation of non-woven webs emanate from the textile industry as a result of taking a very old process such as carding, and combing the textile fibers into a wide web of loose fibers after which they are bonded either chemically or thermally into a consolidated substrate or web. The distribution of these fibers is done mechanically through a series of combing steps in which saw toothed clothed rolls work the fibers into individual strands from clumps and spreads them in the process to form a web. These types of processes lend themselves primarily to textile staple fibers that have fiber lengths of 1 to 2 inches. Even though further evolution of this process has led to the use of air to assist the doffing of the fibers off the main cylinder and in forming a web, these processes do not lend themselves well to short cellulosic fibers which are typically in the 2 to 3 mm in length.
In the mid nineteen sixties and seventies, a combination air and mechanical carding process took the technology further by taking combinations of short cellulosic fibers and longer textile staple fibers combining them mechanically and then air conveying them into a forming chamber so that they could be made into a substrate or web. U.S. Pat. Nos. 3,982,302 and 4,004,323 belonging to Scott Paper describe this process.
The disadvantage of this process was the fact that it was limited to the amount of short cellulose fibers that it could handle. The longer textile staple fibers were still needed to provide an adequate entanglement and fibrous matt structure that would allow to be combed or picked into an air stream for forming.
Both of the carding based processes described so far are depending on the basis weight cross direction profiles of the fibrous matt leading to the forming device. These cross direction profiles are developed and formed prior to the forming step and are somewhat fixed. So if they are not adequate there are no means of correcting of adjusting for them during the formation process. What these forming devices see in cross direction basis weight profile, the substrate or web will get as a result.
A second type of system for forming air-laid webs of dry cellulosic fibers which has found limited commercial use has been developed by Karl Kristian Kobs Kroyer and his associates as a result of work performed in Denmark. Certain of these systems are described in: Kroyer U.S. Pat. Nos. 3,575,749, 4,494,278, 4,014,635 and 5,471,712; Rasmussen U.S. Pat. Nos. 3,581,706 and 3,669,778; Rasmussen et al. U.S. Pat. No. 3,769,115; Attwood et al. U.S. Pat. No. 3,976,412; Tapp U.S. Pat. No. 4,060,360; and, Hicklin et al U.S. Pat. No. 4,074,393.
Hicklin U.S. Pat. No. 4,074,393 shows a funnel like device as the inlet method for the air conveyed fiber to the distributor device which comprises the forming head for this air forming apparatus. It is quite obvious from the construction of the entire forming head, which applies the “fiber sifting” technique for obtaining fiber uniformity in the traverse direction, that the inlet funnel that is used lacks the design features to operate solely as the forming head. The forming device which would ultimately convey the fibers to the forming zone is not this funnel, but the distributor with its multiple rotors. Nowhere in the specification are the details of the design of this funnel like inlet described, as it is quite obvious that they are not key to the overall performance of the forming head described by this invention.
The type of fiber sifting equipment described in the Kroyer patents suffers from poor productivity especially when making light weight webs. For example, the rotor action concentrates most of the incoming material at the periphery of the blades where the velocity is at a maximum. Most of the sifting action is believed to take place in these peripheral areas, while other regions of the sifting screen are either covered with more slowly moving material or are bare. Thus, a large percentage of the sifting screen area is poorly utilized and the system productivity is low. Moreover, fibers and agglomerates tend to remain in the forming head for extended periods of time, especially in the lower velocity, inner regions beneath the rotor blades. This accentuates the tendency of fibers to roll up into pills.
In an effort to overcome the productivity problem of such systems, complex production systems have been devised utilizing multiple forming heads—for example, up to eight separate spaced forming heads associated with multiple hammermills and each employing two or three side-by-side rotors. The most recent sifting type systems employing on the order of eighteen, twenty or more rotors per forming head, still require up to three separate forming heads in order to operate at satisfactory production speeds—that is, the systems employ up to fifty-four to sixty, or more, separate rotors with all of the attendant complex drive systems, feed arrangements, recycling equipment and hammermill equipment.
Honshu, U.S. Pat. Nos. 3,984,898 and 4,160,059, at approximately the same time developed a different concept to the above by combining the fiberization or defibration step into one single step. In this manner the cross direction of the web was dependent on the pulp lap cross-direction profiles feeding the defibrator. The function of the air stream was only to convey the individual fibers onto the foraminous screen to form the web. This process had several disadvantages, as the air stream employed for web forming could not be properly psychometrically conditioned, impacting the quality of the web due to static clumping as a result of very dry fluff fibers.
During the 1970's a series of patents were issued to C. E. Dunning and his associates which have been assigned Kimberly-Clark; such patents describing yet another approach to the formation of air-laid dry fiber webs. Such patents include: Dunning U.S. Pat. Nos. 3,692,622, 3,733,234 and 3,764,451; and, Dunning et al. U.S. Pat. Nos. 3,776,807 and 3,825,381. However, this system requires preparation of pre-formed rolls of fibers having high cross-directional uniformity and is not suitable for use with bulk or baled fibrous materials, such that, to date, the system has not found a commercial application.
Kimberly Clark also developed another fiber air forming process that is described in their U.S. Pat. No. 4,100,324 in which defibrated cellulose pulp is air formed into a molten microfiber meltblown polypropylene stream to form an air laid web without the use of chemical binders. The process described uses the defibrator as the method of conveying the fibers in an air stream into the polypropylene matrix. It is handicapped by the fact that it is a combination defibrator and air former which does neither function well. It is a highly mechanical device which limits the width of the machine based on the width of the defibrator which must span the entire width of the former. The critical speed of the defibrating rotor is the limiter on web forming width limiting it to below two meters typically.
Celli in US Application 20060174452, a few decades later took the same concept as the Kroyer distributor, but re-designed the geometry of the rotors. Rather than having the rotors rotate in the cross direction with their blades parallel to the distributor screens and creating a cross machine direction race track fiber flow inside the distributor, these rotors being cylindrical and rotating in the machine direction with parallel axes, perpendicular to the flow and equipped with radial elements in the form of needles or rods.
Dan Web in U.S. Pat. Nos. 4,278,113, 4,352,649, 4,640,810, 5,885,516 and 7,107,652 in an attempt to differentiate themselves from the Kroyer distributors in which they claimed parallel interfaces between the distributor screen geometries and the foraminous forming screen, developed a similar concept distributor but in a round drum-shaped geometry. This former head, where a fiber material mixed with air is conducted to at least one rotating perforated drum in a former head by injection, has internally fluidizing means constituted by air nozzles arranged longitudinally of the drum with the air being controlled longitudinally. Again, in this case the cross direction distribution of fibers is accomplished by the trajectory of the fibers inside the rotating drum formers, and the air system's primary purpose is only to convey the fibers to the forming screen.
Other devices have been developed in an attempt to spread fibers and or particles uniformly across the width of various forming zones. These apparatus may at first hand appear similar in nature and principle to the invention disclosed but at close scrutiny do not have the same design characteristics and would not work with the degree of efficiency as the professed invention. They also would suffer severely from great width capability limitations.
Marshall, U.S. Pat. No. 3,863,867, discusses a funnel like apparatus that is primarily designed to randomize the machine and cross direction formation of textile fibers of 1-2 inches in length through centrifugal force. This type of device uses diffusion of air flows as a primary means of fiber control and submits the fiber and air stream to areas of increased and reduced air velocities inside the apparatus which would result in turbulence and impact the cross-direction uniformity of the fibers. These techniques would not work at all in distributing the fibers to the forming section with short cellulose fibers which are the primary component of our fiber stream as the turbulence in the air stream would not provide the uniform distribution required in the cross direction.
Thorbjörnsson, U.S. Pat. No. 4,688,301, and Gustavsson, U.S. Pat. No. 4,269,578 also use a funnel like apparatus to distribute fibers from an inlet duct to a wider forming chamber. In both cases, they use either a mechanically oscillating device or an air pulsing device to spread the fibers evenly in the cross direction. Even though these types of devices have been used successfully in the textile industry with staple fibers, the speed of fiber distribution inside the spreading device will not be able to keep up with the throughput requirements of the forming device for high speed short fiber airlaid non-woven forming processes.
Kock, U.S. Pat. No. 4,551,191, another funnel like device was developed to handle particulate and not fibrous matter. It is composed of three segments involving 30 degree stepped angle changes in which the air velocity is increased, and with the three straight sections utilizing a riffling surface to spread the particles. This type of device, as it was primarily intended for particles, will create pilling as described earlier through the use of the riffling surfaces. Also, the device requires a change in direction as one of the means of spreading, which for light weight fibers will provide sufficient turbulence to affect the cross direction profile of the light weight fibers negatively.
Indeed, heretofore it is not believed that any of the previous air-forming techniques can be advantageously used in high speed production operations to prepare cellulose fiber sheet material that are sufficiently thin, and have adequate cross-directional profiles at high forming speeds to satisfy the performance requirements of the final product application.